Blow-molded plastic boxes of double-wall construction are widely used where economy, durability and light weight are desired. The light weight reduces shipping costs, and the double-wall construction provides cushioning against shocks. One such box for tape cassettes is shown in U.S. Pat. No. 4,078,657. The detailed construction of its hinge is not illustrated, but a box essentially as illustrated in the patent has been on the market for several years. Extending along the rear of the base of the box is a hollow, upstanding spine which terminates in a pair of hinge pins that fit into holes drilled into the cover. In commercial production, the box is assembled soon after its parts are molded and while they are still warm and supple. The cover is placed in a fixture which spreads the holes apart slightly, and the assembler grasps the base and forces it into the fixture which bends the base of the box at the spine in order to bring the hinge pins closer together. As the hinge pins move into alignment with the holes, the bending force is released and the hinge pins snap into place. The hinge of the box which has been on the market has a lateral looseness which may not have been objectionable.
A similar hinge is used on another blow-molded, double-wall plastic box and shown in greater detail in U.S. Pat. No. 4,005,800.